One conventional electrophotographic image forming apparatus is a printer that includes a main casing; a drum unit that is detachably mounted in the main casing and provided with a photosensitive drum and a charger; a developing cartridge that is detachably mounted in the drum unit and provided with a developing roller; and an exposure device that exposes the photosensitive drum.
In this type of printer, the charger first applies charge to a surface of the photosensitive drum, after which the exposure device selectively removes charge from the surface of the photosensitive drum to form an electrostatic latent image thereon. Next, the developing roller supplies toner to the electrostatic latent image on the photosensitive drum to form a toner image thereon. The toner image is then transferred from the surface of the photosensitive drum onto paper to form an image on the paper.
However, occasionally electric charge that remains on the surface of the photosensitive drum after a toner image has been transferred from the photosensitive drum to paper affects the next electrostatic latent image formed on the surface of the photosensitive drum, leading to poor image formation quality. Therefore, studies have been conducted on how to remove electric charge from the surface of the photosensitive drum.
For example, one printer that has been proposed includes a rod-like light guide that is supported in a drum unit so as to be opposite a surface of a photosensitive drum while extending in a left-right direction, and a light source disposed in a main casing on the right side of the light guide.
In a printer having this construction, light emitted from the light source enters the light guide through its right endface and is guided by the light guide to be irradiated onto the surface of the photosensitive drum. This irradiated light removes any residual charge from the surface of the photosensitive drum.